High frequency oscillator



Aug. 18, 1936. G. A. HOBART. 3D 2,051,601

HIGH FREQUENCY OSCILLATOR Filed. March 28, 1934 IONIZABLE mx MED/UM I z; 26 J Inventor: Garret A. Hobart 3d His Attorney.

Patented Aug. 18, 1936 UNITED STATES PATENT OFFICE HIGH FREQUENCY OSCIILA'IOB Garret a. Hobart, so, Schenectady, N. 1., assignor to General Electric Company, a corporation of New York My invention relates to high and ultra-high frequency oscillators, and more particularly to such oscillators utilizing electric discharge devices containing an ionizable medium.

In the copending applications of Irving Langmuir, Serial No. 717,747, and Lewi Tonks, Serial No, 717,741,,both filed concurrently herewith and assigned to the same assignee as the present application, there are disclosed and claimed high frequency oscillators utilizing an electric discharge device having an envelope containing an ionizable medium, an anode, a cathode and a grid element. This ionizable medium is at a pressure sufiicient to permit ionization of such degree as to form a plasma, but yet not great enough to impede seriously the free motion of electrons. The grid element of this discharge device, which is sumciently large to divide the envelope into anode and cathode compartments, is charged negatively so as to maintain a substantially continuous positive ion sheath about the grid. This grid separates the ionizable medium into cathode and anode plasmas. The positive ion sheath about the grid element is capable of preventing or inter- 5 rupting an electron fiow between the two plasmas up to the immediate proximity of the grid. At

this time, the electrons from one plasma pass through the grid to the other plasma. By means 5 of this electric discharge device continuous oscillations of high and ultra-high frequencies may be generated at a relatively high efliciency so as to produce a high intensity output.

My invention relates to a high frequency oscillator of a type disclosed in the aforementioned applications, and an object of my invention is to provide an improved modification of the arrangements disclosed therein, by means of which still higher frequency oscillations may be attained.

It is another object of my invention to provide an improved electric discharge device.

In accordance with my invention, there is provided an electric discharge device having an envelope which contains an anode, a cathode, a grid element and an ionizable vapor at a pressure sufmember, or metallic band, is provided as means for coupling capacitively a portion of the circuit to the cathode plasma. A plurality of similar metallic members are provided in the vicinity of the anode to operate as capacitive coupling means between circuits and the anode plasma. If a circuit is connected between the cathode plasma coupling means and the grid or one of the anode plasma metallic bands and this circuit is tuned to a certain frequency, it has been found that a second circuit connected between the metallic bands at'the anode plasma may be tuned to a multiple of the frequency of the first circuit. Oscillations of sufiicient intensity will be generated in the second circuit so that an output circuit may be coupled to this circuit.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood by reference to the following description taken in connection with the accompanying drawing in which the figure represents an oscillator embodying my invention.

Referring to the drawing, I have illustrated therein an oscillator utilizing an electric discharge device Hi. This discharge device l0 comprises an anode II, a cathode [2, a grid element l3, all enclosed within an envelope H which also contains an ionizable medium at a pressure just sufiicient to permit an ionization necessary to allow plasma to form, yet not of sufficient pressure so as to impede materially or seriously the free motions of electrons. This ionizable medium may comprise a small amount of mercury, or one of the rarer gases such as argon, neon, or helium. The mercury vapor is at a pressure within the range of 0.1 to 2 microns while the neon and helium'gases are at a pressure of the order of one millimeter of mercury. The gridelement i3 is preferably of a fine wire mesh and is of such configuration or magnitude as to separate adequately the anode plasma from the cathode plasma. It is to be understood that the grid element need not extend to the walls of the envelope, inasmuch as any configuration which will separate adequately the anode plasma from the cathode plasma will suffice. One example of such grid configuration would be a cylindrical grid closed at one end and located so as to enclose substantially either the anode or the cathode, and this grid need not extend to the'walls of the envelope. A circuit extending from the cathode I! to the anode Ii includes a source of potential I! for supplying current to the anode and an inductor choke I8 for preventing high frequency current from being dissipated in this circuit. A circuit extending from the grid element I! to the cathode l2 includes a. portion of the inductor II, a choke inductor It for preventing high frequency currents from being dissipated in this circuit, and means for placing a charge upon the grid I! which is at least negative with respect to the anode and in this instance is shown to be a source of potential I9. The negative charge placed upon thegrid element It by the source of potential l9 causes a substantially continuous positive ion charge to be formed about the grid it which separates the ionizable medium into anode and cathode plasmas. These plasmas are generally defined in the art'as being an electrically neutral body of an ionized medium. By means of the positive ion sheath about the grid, this grid element is capable of controlling or interrupting the fiow of electrons between the anode and cathode plasmas.

The grid to cathode plasma circuit comprises a connection from the grid l3, a portion of the inductor l7 and a connection from this inductor to a conductive member or metallic band 20, which serves as a capacitive coupling means to the cathode plasma. A second circuit from the cathode plasma to the anode plasma comprises a connection from the conductive member 20, the remainder of the inductor l1 and a connection to a metallic band 22. In order to tune at least one of these circuits a variable capacitor 2| is connected between the extremities of the inductor I1. A certain amount of the high frequency energy present in the second circuit is transmitted to the first circuit which, it will be remembered, was the circuit from the grid II, a portion-of the inductor l1 and a connection to the metallic band 20. In the instance shown, this transfer of energy is accomplished by the conductive connection between the two portions of the inductor l|. It is to be understood, however, that these circuits may be entirely separate and inductive or capacitive coupling may be used for the transfer of energy between these two circuits. This transfer of energy causes oscillations to be set up, the frequency of which is determined by the resonance of the circuit including the inductor l1 and the capacitor 2 I. A third metallic, or conductive member 23 is provided at the upper extremities of the anode plasma compartment. These conductive, or metallic bands 20, 22 and23, which serve as capacitance coupling means to the cathode and anode plasmas, need not be contiguous to the envelope and may comprise metallic strips partially or totally surrounding the envelope H of the discharge device iii. A third circuit is connected between the conductive bands 22 and 23 and comprises an inductor 25 and a variable capacitor 24. The circuit comprising the inductor 25 and the capacitor 24 is preferably tuned to the second harmonic, or any other multiple, of the frequency of the resonant circuit which comprises the inductor l1 and the capacitor 2|. In order to utilize the high frequency energy in the circuit 24, 25, an output circuit is coupled to the inductor 25 and this output circuit may comprise an inductor 26 which may be connected to a dipole antenna as shown, or any other utilization circuit.

In order to cause formation of plasma. and to initiate the generation of oscillations, it is necessary to provide some means selectively operable for momentarily overcoming the effect of the negative charge impressed upon the grid I! by the source of potential II. This means may comprise, for example, a circuit from the cathode II to the grid l2 including a source of potential 21 for impressing a positive potential upon the grid I3 and a switch 28. When the switch 20 is closed. a positive potential will be impressed upon the grid it which therefore will reduce or neutralize the effect of the positive ion charge on the grid with the result that electrons will pass from the cathode plasma to the anode plasma. When the switch 28 is again opened a certain amount of transient energy will have been stored in the circuit i1, 2|. Thistransient energy will cause a variation of the positive ion charge upon the grid II with the result that a momentary flow of electrons will occur from the cathode plasma to the anode plasma. This momentary fiow of electrons will be followed by other flows of electrons due to variations of the charge upon the grid II, the

frequency of which will be determined by theresonant frequency of the circuit II, 2i.

While a complete theory of theoperation of the entire circuit has not been developed, it has been found that by tuning the circuit 24, 25 to a harmonic of the resonant frequency of the circuit l1, 2 I, oscillations of much higher frequency may be obtained from an electric discharge device of this type than, it is believed, has been possible heretofore.

While I have shown and described my invention in connection with certain specific embodiments, it will, of course, be understood that I do not wish to be limited thereto, since it is apparent that the principles herein disclosed are susceptible of numerous other applications, and modifications may be made in the circuit arrangement and in the instrumentalities applied without departing from the spirit and scope of my invention, as set forth in the appended claims.

What I claimas new and desire to secure by Letters Patent of the United States, is,

1. A high frequency oscillator including a discharge device comprising anode, cathode and grid elements within an envelope containing an ionizable medium at a pressure sufficient to permit ionization without material impediment to electron movement, a circuit including a source of potential connected between said anode and said cathode, means for impressing a potential upon said grid to produce normally a substantially continuous positive ion sheath around said grid, said grid having such configuration as to separate said envelope into anode and cathode compartments, a plurality of means for capacitively coupling circuits to said anode compartment, means for capacitively coupling circuits to said cathode compartment, a circuit connected between said grid and said cathode compartment coupling means, a second circuit connected between one of said anode compartment coupling means and said cathode compartment coupling means, means for tuning at least one of said circuits, a circuit connected between said anode compartment coupling means, and an output circuit coupled to said last circuit.

2. A high frequency oscillator including a discharge device comprising an envelope containing an anode, a cathode, a grid element and an ionizable medium at a pressure sufiicient to permit a' degree of ionization offering no substantial impediment to free electron motion, a source of potential connected between said anode and said cathode, means for impressing a potential upon said grid to produce normally a substantially continuous positive ion sheath around said 8 75 said grid having a configuration sumcient for separating said ionizable medium into anode and cathode plasmas, a circuit capacitively coupled to said cathode plasma and connected to said grid element, a second circuit capacitively coupled to said cathode plasma and capacitively coupled to said anode plasma in the proximity of said grid, means for tuning at least one of said circuits to a certain frequency, and a third circuit capacitively coupled-to different portions of said anode plasma, said circuit being tuned to a harmonic of the frequency of said other tuned circuit, an output circuit coupled to said third circuit.

3. A high frequency oscillator including a discharge device comprising an envelope containing an anode, a cathode, a grid element, and an ionizable medium at a pressure sufiicient to permit member capacitively coupled to said cathode plasma, a plurality of metallic members capacitively coupled to said anode plasma, a circuit connected between said grid and said cathode metallic member, a second circuit connected between said cathode metallic member and one of said anode metallic members, means for tuning at least one of said circuits to a certain frequency, means for transferring a portion of the energy of said second circuit to said first circuit, a third circuit connected between said anode metallic members, said circuit being tuned to a multiple of said other tunedcircuit, an output circuit coupled to said third circuit, and means selectively operable for neutralizing the effect of said means for producing said positive ion sheath.

4. A high frequency oscillator including a discharge device comprising an envelope containing an anode, a cathode, a grid element and an ionizable medium at a pressure sufilcient to permit ionization without material impediment to free electron movement, an anode means for producing a plasma surrounding said anode and a cathode plasma surrounding said cathode, a conductive member capacitively coupled to said cathode plasma, a plurality of conductive members coupled to said anode plasma, said latter members being in spaced relation to each other, means for producing normally a positive ion sheath about said grid normally to restrict the flow of electrons between said plasmas, an anode cathode circuit including a source of potential and means for preventing high frequency energy from entering said circuit, a circuit connected to said grid and to said cathode plasma conductive member, a second circuit connected to said cathode plasma conductive member and one of said anode plasma conductive members, means for tuning at least one of said circuits to a certain frequency,

means for transferring energy from said. second circuit to said first circuit whereby said positive ion sheath will be altered periodically to cause a flow of electrons between said plasmas, a third circuit connected between said spaced anode plasma conductive members, means for tuning said third circuit to a multiple of the frequency of said first tuned circuit, and an output circuit coupled to said latter tuned circuit.

5. An electric discharge device comprising an envelope containing an anode, a cathode and a grid element, said grid element having such configuration and magnitude as to divide said envelope into anode and cathode compartments,

and a plurality of arcuate metallic members mounted exteriorly adjacent to said envelope in the proximity of said anode.

6. An electric discharge device comprising an envelope containing a grid'element, a cathode at one end, and an anode at the other end, a plurality of metallic members mounted exteriorly adjacent to said envelope, one of said metallic members being located in the proximity of said cathode, another of said metallic members being located in the proximity of said anode end of said envelope, and a third metallic member located intermediate said other two members.

7. An electric discharge device comprising an envelope containing a grid element, a cathode at one end, and an anode at the other end, said grid element having such configuration and magnitude as to divide said envelope into anode and cathode compartments, and a plurality of metal members mounted on the exterior of said envelope, one of said members being located at the anode end of said envelope, and the other of said members being located between said anode and said grid element.

8. An electric discharge device comprising an envelope containing an ionizable medium at a pressure sufiicient to support ionization without material impediment to the motion of free electrons, an anode, a-cathode and a grid element, said grid element having such configuration as to divide said envelope into anode and cathode compartments, and a plurality of metal members mounted exteriorly adjacent to said envelope in I GARRET A. HOBART, 3D. 

